1. Field of the Invention
The present invention relates to an image acquisition apparatus which acquires a fundus image and a tomographic image of an eye to be inspected.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2007-252693 discloses an apparatus which partially integrates an optical system of optical coherence tomography (OCT) for acquiring a tomographic image of an eye to be inspected with an optical system of a fundus camera (an apparatus for acquiring a two-dimensional (2D) image of a fundus by visible light). In particular, when an operation button of a joystick provided on the fundus camera is pressed, a plurality of 2D tomographic images (known as cross-sectional or B-scan images) is acquired and then a fundus image is acquired by visible light as illustrated in FIG. 6A and the like.
In general, the observation pupil diameters (the diameter of a beam emitted on an anterior ocular segment of an eye to be inspected) of the OCT optical system and the fundus camera optical system are about 1 mm and 4 mm respectively. In other words, the beam diameter of the fundus camera is larger than that of the OCT.
Here, a case is considered in which the anterior ocular segment to be imaged of the eye to be inspected has a partial haze caused by a cataract or the like near the ocular axis. At this time, when a tomographic image is acquired by aligning the optical axis of an illumination optical system with the ocular axis of the eye to be inspected, the irradiation light is blocked at the place in which the anterior ocular segment has a haze. Thus, a dark tomographic image is acquired. In light of this, the inspector may try to acquire a bright tomographic image by aligning the fundus with a non-blocked section of eye. This may be performed by observing the anterior ocular segment and shifting the optical axis of the illumination optical system away from the ocular axis.
As a result of this, however, there is a problem in that when a fundus image is acquired in a state in which the optical axis of the illumination optical system is shifted away from the ocular axis after the tomographic image is acquired, the irradiation light toward the anterior ocular segment causes vignetting or the like in the iris of the anterior ocular segment. In other words, while tomographic imaging may be successful even when the axes are not aligned, fundus imaging does require more careful aligning of the measurement beam with the fundus of the eye. Thus, generally, after a tomographic image is acquired, the inspector acquires a fundus image by aligning the optical axis of the illumination optical system with the ocular axis again.
However, if, after the tomographic image has been acquired by shifting the optical axis away from the ocular axis, the amount of shift of the optical axis from the ocular axis is small enough not to cause the vignetting in the fundus image after all, there may be no need to realign the optical axis of the illumination optical system with the ocular axis before the fundus image is acquired. Thus, the user of the apparatus (hereinafter, the inspector) may have wasted time in realigning the axes prior to beginning the fundus imaging. On the other hand, it may be very cumbersome for the inspector to determine whether or not alignment is required before the fundus imaging after the tomographic imaging, causing a reduction in diagnostic efficiency. It has thus been more efficient simply to realign the axes every time, prior to fundus imaging.